From: Junichi Nomura <j-nomura@ce.jp.nec.com>
Date: Thu, 1 Oct 2015 08:31:51 +0000 (+0000)
Subject: dm: fix AB-BA deadlock in __dm_destroy()
X-Git-Tag: v3.16.35~1158
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=e762d4813b22d354245d03b85455e27197f3ad45;p=thirdparty%2Fkernel%2Fstable.git

dm: fix AB-BA deadlock in __dm_destroy()

commit 2a708cff93f1845b9239bc7d6310aef54e716c6a upstream.

__dm_destroy() takes io_barrier SRCU lock (dm_get_live_table) and
suspend_lock in reverse order.  Doing so can cause AB-BA deadlock:

  __dm_destroy                    dm_swap_table
  ---------------------------------------------------
                                  mutex_lock(suspend_lock)
  dm_get_live_table()
    srcu_read_lock(io_barrier)
                                  dm_sync_table()
                                    synchronize_srcu(io_barrier)
                                      .. waiting for dm_put_live_table()
  mutex_lock(suspend_lock)
    .. waiting for suspend_lock

Fix this by taking the locks in proper order.

Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Fixes: ab7c7bb6f4ab ("dm: hold suspend_lock while suspending device during device deletion")
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b3fdf9cfbeb94..91b2394897857 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2413,7 +2413,6 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
 	might_sleep();
 
 	spin_lock(&_minor_lock);
-	map = dm_get_live_table(md, &srcu_idx);
 	idr_replace(&_minor_idr, MINOR_ALLOCED, MINOR(disk_devt(dm_disk(md))));
 	set_bit(DMF_FREEING, &md->flags);
 	spin_unlock(&_minor_lock);
@@ -2423,14 +2422,14 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
 	 * do not race with internal suspend.
 	 */
 	mutex_lock(&md->suspend_lock);
+	map = dm_get_live_table(md, &srcu_idx);
 	if (!dm_suspended_md(md)) {
 		dm_table_presuspend_targets(map);
 		dm_table_postsuspend_targets(map);
 	}
-	mutex_unlock(&md->suspend_lock);
-
 	/* dm_put_live_table must be before msleep, otherwise deadlock is possible */
 	dm_put_live_table(md, srcu_idx);
+	mutex_unlock(&md->suspend_lock);
 
 	/*
 	 * Rare, but there may be I/O requests still going to complete,